Reconstitution of T cell receptor zeta-mediated calcium mobilization in nonlymphoid cells.

T cell antigen receptor (TCR) activation involves interactions between receptor subunits and nonreceptor protein tyrosine kinases (PTKs). Early steps in signaling through the zeta chain of the TCR were examined in transfected COS-1 cells. Coexpression of the PTK p59fynT, but not p56lck, with zeta or with a homodimeric TCR beta-zeta fusion protein produced tyrosine phosphorylation of both zeta and phospholipase C (PLC)-gamma 1, as well as calcium ion mobilization in response to receptor cross-linking. CD45 coexpression enhanced these effects. No requirement for the PTKZAP-70 was observed. Thus, p59fynT may link zeta directly to the PLC-gamma 1 activation pathway.